JPH04260209A - High frequency amplifier - Google Patents

Abstract

PURPOSE:To considerably adjust the level of the gain of one high frequency amplifying element to be by-passed, to simplify the circuit, and to obtain a stable output level even at the time of reduction of the output level by eliminating a need of a gain variable circuit and a gain control circuit which are required in a conventional example and always keeping the output level of a high frequency amplifying element in the preceding stage of a switching circuit. CONSTITUTION:A line switch 3 which selects whether a high frequency amplifying element 6 in the succeeding stage should be connected or by-passed and a switch control circuit part 4 which controls this line switch by a request signal from the external which reduces the output-side high frequency level are provided between a high frequency amplifying element 2 in the preceding stage and the high frequency amplifying element 6 in the succeeding stage.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency amplifier, and more particularly to a high frequency amplifier having an improved level variable circuit provided at a microwave output section.

0002

2. Description of the Related Art Conventionally, an output level variable circuit for a high frequency amplifier of this type has a high frequency amplification element 12 as shown in FIG.
, 13, and bias voltage control circuits 14, 15 that control the bias voltages of the high frequency amplification elements 12, 13. Another conventional example, as shown in FIG. 4, includes high frequency amplification elements 16 and 18, a variable gain circuit 17 for attenuating the high frequency signal at the output section of the high frequency amplification element 16, and a gain control circuit that performs variable gain control. It has 19.

Next, the operation will be explained. The high frequency amplification element shown in Fig. 3 is generally a high frequency amplification element of class B or C operation such as a common base type bipolar transistor. Variable level saturation output. Generally, the output level of the final stage high frequency amplification element 13 is controlled by a bias voltage control circuit 15. FIG. 4 shows the high frequency amplification element 16
, 18 is an example of a high frequency amplifier with a variable output function when a high frequency amplification element of class A operation such as a GaAsFET is used, and the bias current or bias voltage of the variable gain circuit 17 is changed by the gain control circuit 19. By controlling the attenuation amount of the variable gain circuit 17, the high frequency amplifying element 18
By increasing or decreasing the input signal level, the output level is increased or decreased.

0004

[Problem to be Solved by the Invention] In the conventional variable output level circuit of a high frequency amplifier, in the former case, the level is varied by controlling the bias voltage of the high frequency amplification element, and in the latter case, the level is varied by controlling the attenuation amount of the variable gain circuit. Therefore, it is not possible to reduce power consumption when the output level decreases. Particularly in the case of the configuration shown in FIG. 3, the level variable range is small. Further, as shown in FIG. 3, if bias control is performed on two or more elements, not only the circuit configuration becomes more complicated, but also the stability of the output level with respect to temperature deteriorates. Furthermore, since both conventional examples must each include a bias voltage control circuit, a gain control circuit, etc., the circuit structure becomes complex and large in size.

[0005]

[Means for Solving the Problems] The high-frequency amplifier of the present invention provides a high-frequency signal that selects whether to connect or bypass the high-frequency amplification element in the latter stage between the high-frequency amplification element in the former stage and the high-frequency amplification element in the latter stage. It has a switching section and a switching device control circuit section that controls the high frequency signal switching section based on an external request signal that lowers the output side high frequency level.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment of the present invention. A high frequency signal switching section 3 and a switch control circuit section 4 are provided between the high frequency amplifying element 2 and the high frequency amplifying element 6 to perform switching control of the high frequency signal switching section 3. The high frequency signal switching section 3 selects either the main line 5 connected to the input section of the high frequency amplification element 6 and the bypass line 7 connected to the output section by bypassing the high frequency amplification element 6. When it is desired to obtain a normal output level, the high frequency signal line switching section 3 selects the main line 5 side and sends the output of the high frequency amplification element 6 to the output terminal 8 as it is. Here, the bypass line 7 has an electrical line length of 1/2 from the output side connection point of the high frequency amplification element 6 to the open contact point of the high frequency signal switching section 3.
Since the wavelength is set so that the main line 5 is not affected in any way. Furthermore, when lowering the output level, the high frequency signal switch 3 is selected to the bypass line 7 side and the high frequency amplification element 6 is bypassed, so the output level can be lowered by the gain of the high frequency amplification element.

FIG. 2 is a block diagram of a second embodiment of the invention. The difference between the second embodiment and the first embodiment is that the high frequency amplification elements 2 and 6 are also provided with bias voltage control circuits 9 and 10, respectively, and the high frequency signal switching section 3 of the first embodiment is The circuit configuration uses a high frequency relay 11. In the second embodiment, the main output level with a narrow variable range is set by the high frequency amplifying element 6 by the bias voltage control circuit 10, and when a large output level drop is required, the high frequency relay 11 is set by the switching control circuit section. 4 to bypass the high frequency amplification element 6 and lower the output level. In order to further adjust the output level that has been lowered, the bias voltage control circuit 9 of the high frequency amplification element 2 performs fine adjustment settings. In addition, when a base-grounded bipolar transistor or the like is used as the high-frequency amplification element, if the switching circuit is selected on the bypass line side,
Since the input signal is no longer driven to the bypassed high-frequency amplification element section and the collector current no longer flows, it is possible to reduce power consumption when the output level decreases.

[0009]

As explained above, the present invention provides a switching circuit for the main line and the bypass line of the subsequent high-frequency amplification element between two high-frequency amplification elements to vary the output level. It is possible to significantly adjust the level of the gain of the high frequency amplification element. Further, unlike the conventional example, a variable gain circuit and a gain control circuit are not required, so the circuit can be simplified. Furthermore, since the output level of the high-frequency amplifying element before the switching circuit is always in a saturated state, a stable output level can be obtained even if the output level is lowered. Further, when a common base type transistor is used as the high frequency amplification element and the high frequency amplification element is bypassed, it is possible to reduce the power consumption of this amplification element.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a high frequency amplifier showing a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment of the invention.

FIG. 3 is a block diagram of a first example of a conventional frequency amplifier.

FIG. 4 is a block diagram of a second example of a conventional high frequency amplifier.

[Explanation of symbols]

1 Input terminals 2, 6 High frequency amplification element 3 High frequency signal switching section 4 Switch control circuit section 5 Main line 7 Bypass line 8 Output terminals 9, 10 Bias voltage control circuit 11 High frequency relay

Claims (3)

[Claims] 1. A high-frequency signal switching unit for selecting whether to connect or bypass the latter-stage high-frequency amplification element between the former-stage high-frequency amplification element and the latter-stage high-frequency amplification element, and reducing the output side high-frequency level. and a switch control circuit section that controls the high frequency signal switching section based on a request signal from the outside. 2. The high-frequency amplifier according to claim 1, wherein the level of each of the front-stage high-frequency amplification element and the second-stage high-frequency amplification element is controlled by a bias voltage control circuit that finely adjusts the output level. 3. The length of the bypass line connecting the output section of the high-frequency amplification element in the subsequent stage and the bypass terminal of the high-frequency signal switching section is approximately 1/2n (
2. The high frequency amplifier according to claim 1, wherein n is an integer) and a line length of a wavelength.